1. Field of the Invention
The present invention relates to a shift register, and more particularly, to a bidirectional shift register which is capable of preventing multi-outputs from both end stages.
2. Discussion of the Related Art
A bidirectional shift register, which is capable of outputting scan pulses forward or reversely, includes a plurality of stages. In particular, a start pulse is always supplied to a first stage and a last stage at the beginning of driving irrespective of forward driving or reverse driving.
For this reason, in the forward driving, a set node of the last stage floats by the start pulse, resulting in a multi-output problem that the last stage outputs two scan pulses for one frame period. Likewise, in the reverse driving, a set node of the first stage floats by the start pulse, resulting in a multi-output problem that the first stage outputs two scan pulses for one frame period.
As a result, a last gate line connected to an output terminal of the last stage is periodically driven, thereby causing pixels connected to the gate line to emit light with higher luminance than other pixels. In particular, when data corresponding to black is supplied to all pixels with light emitting elements, an end line brightening phenomenon occurs in which pixels connected to an end line become brighter than pixels connected to other gate lines. This phenomenon is more prominent at a high temperature at which the threshold voltage of a pull-up switching device is liable to be shifted.